Welcome! It can be overwhelming if you want it to. Keep it fun, and remember how it will be when you get it like you want it. Every day I step outside, it's like a little kid finding the cool present under the Christmas tree.
Mine was pretty rough when I got it, and the first order of business was to clean it. top to bottom, front to back. Outside top to bottom. Then I did it again.
Each time you go over an area that you don't like, you will get a better sense of what needs to be done. If you have carpet/padding, remove it. You will be able to see water damage a little easier, and more closely find the source of the leak.
If you don't have an owners manual, you can get one at Airstream. It gives an overview of how all the systems work.
You can break down your "to do" list by system, Electrical, Plumbing, etc. and work out what you need, how much it will cost.
Keep this list, it will be a source of encouragement as time goes on.
It's a matter of setting priorities as you care to, and working your way through the list. It's your Awesome Airstream, and it will be even better when you are done.
There are several very good vendors for AS parts. I have used Vintage Trailer Supply for parts to fix my original door lock that everyone said was unfixable. Silver Trailer Supply has all the small pieces like the glides for the fold out bed and others.
Something else that I have found to be helpful is a printed catalog. You can go to your nearest RV/trailer dealer and ask for a hard copy of their catalog. Most of the generic parts can be found here and it supports a local business. Tell them what you are doing and they most likely will be able to cheerfully help you out. You can get an ball park idea of repairs cost that you cant or don't want to do.
Finding and fixing the leaks would be my first priority, followed by floor repairs.
The front and rear flooring is prone to water infiltration where the seal/skin meet at the frame rails.
Always remember to have fun with YOUR Airstream. It's going to be awesome.